We have been working on the second version of our 3-D visualization software, IMOD. The first version is described in a published volume on image processing software [Kremer, J. R. Mastronarde, D. N. McIntosh, J. R. (1996) Computer Visualization of Three-Dimensional Image Data Using IMOD. J. Struct. Biol. 116, 71-76]. The second version has now been released after seven beta releases. Several improvements, bug fixes and speed optimizations have been implemented during the beta testing phase. IMOD now runs routinely on three different platforms in our department, SGI, Sun and Dec Alpha. We have also released IMOD source code to non-profit groups, and so far 7 groups have access to the source code. As of July 1st IMOD is distributed through our web site at http//bio3d.colorado.edu/imod/. Previous to that our software was available from our ftp server, which kept inprecise records of the number of downloads. During the month of July, 7 people downloaded the SGI version, one person downloaded the SUN version, and one person downloaded the VMS version of our software. Independent control plug-in-modules can enhance the usability of IMOD, and several new modules have been developed. An automated contour generator based on line tracking and one based on cross-correlation have been developed. A group of plug-in-modules used for automated modeling and lineaging of C. elegans embryos are in the process of being developed. Plug-in modules for reading different types of image formats are also under development. [unreadable]